The present invention relates to the field of focused ion beam (FIB) systems, and in particular, to multi-column FIB systems providing high throughput for milling, enhanced etch, and deposition applications.
Thin film head trimming and other nanofabrication applications suffer from throughput limitations, that is, the focused ion beam systems are unable to process products as quickly as desired. One approach to increasing processing speed is to increase the current in a given beam, thereby increasing the rate at which material is removed or deposited. Unfortunately, systems are approaching fundamental limits for beam current within the small beam diameters required.
Another solution to increasing throughput is simply to use additional FIB systems. Because FIB systems are complex and include a variety of subsystems, each individual system is costly.
To increase throughput in electron beam lithography and semiconductor inspection areas, researchers have begun using multiple electron field emitters or photoemission sources in a single system. For example, multiple electron beam systems are described in U.S. Pat. No. 4,390,789 to Smith for xe2x80x9cElectron Beam Array Lithography System Employing Multiple Parallel Array Optics Channels and Method of Operationxe2x80x9d and U.S. Pat. No. 5,981,962 to Groves et al. for a xe2x80x9cDistributed Direct Write Lithography System Using Multiple Variable Shaped Electron Beams.xe2x80x9d
These multi-beam electron beam system designs do not readily transfer to ion beam systems because the ion optical columns operate at much higher voltages and therefore present design problems that are not present in electron beam systems. Designing an array of high voltage FIB columns that operate at beam voltages of about +30,000 V presents problems that are quite different from those involved in designing an array of electron beam columns, which typically operate between about xe2x88x92500 to xe2x88x925000 V, for lithography or inspection. Moreover, the higher voltage power supplies are bulkier and more costly than low voltage ones required for electron beam systems, making it difficult to produce a compact and competitively priced multicolumn FIB system.
U.S. Pat. No. 5,945,677 to Leung et al. for a xe2x80x9cFocused Ion Beam Systemxe2x80x9d describes two approaches for multiple ion beam systems using one or more plasma ion sources. In the first approach, a single multicusp plasma ion source is used to produce multiple beamlets. The second approach employs multiple FIB units, each having a separate ion source and acceleration column. Such systems are complex, and no large area source, multiple column systems are currently commercially available. Furthermore, multicusp sources, which are about 100 times less bright than liquid metal field ion sources, have so far not achieved sufficient brightness to be commercially practical.
Thus, a practical, cost effective solution for increasing focused ion beam throughput while maintaining resolution is still needed.
An object of the present invention is to increase processing speed for nanofabrication without sacrificing processing precision by providing a precision multi-column FIB system.
The present invention includes a method of increasing the throughput of a FIB system, a FIB system capable of increased throughput, and a method of making and using the FIB system. The invention also includes several novel aspects of the FIB system, including the modular design of the gun chambers, the design of the electrodes, including their electrical isolation, the secondary particle collection system, and the electrode voltage application scheme.
A FIB system of the present invention comprises multiple ion guns, each preferably including a Liquid Metal Ion Source (LMIS) and associated with a corresponding FIB optical column. The beams from the multiple columns are directed to one or more targets in a primary vacuum chamber. The multiple guns increase the number of ions impacting the target or targets and therefore increase the processing rate. For example, the multiple beams can operate on different wafers, or on different parts of a single wafer, with the wafer or wafers being in a single primary vacuum chamber. Because each of the multiple columns has substantially the same resolution and beam current as that of a column in a single gun FIB system, accuracy and precision is not degraded as processing speed is increased. Because the multiple columns share a primary vacuum chamber and can share other facilities, such as power supplies, a computer and a user interface, the initial cost and operating cost of a system of the invention is greatly reduced compared to the costs associated with multiple, separate complete FIB systems.
Preferably, each FIB gun is placed in a vacuum chamber, referred to as a gun chamber, that can be evacuated independently from the primary vacuum chamber. Multiple such gun chambers, each containing one or more FIB guns, can be placed in parallel to form a large array of guns for operating on one or more targets in the primary vacuum chamber. A common, ganged vacuum valve for each gun chamber can isolate the gun chamber from the main chamber. Moreover, the gun chambers can be evacuated and sealed prior to installation, thereby avoiding the loss of production that would occur if the gun chamber were evacuated after installation. By separating the gun chamber or chambers from the main chamber, gun chambers can be replaced without disrupting the vacuum in the main chamber, thereby avoiding the introduction of contaminants and saving the time required to re-evacuate the main chamber. By having guns in separate gun chambers, some guns can be replaced without disturbing others. A gun chamber can be replaced as a module in the field, with the repairs or replacements of individual guns being performed at the factory.
Each gun has a corresponding ion optical column, with some of the column elements preferably being placed below the guns in the main system chamber to form an array of columns. To reduce complexity and to increase the placement precision between columns, column elements can be made common between the columns by using bars with precision cut holes to form the lens elements.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.